The present invention relates generally to aircraft gas turbine engine augmentors and, more specifically, to radial flameholders and spray bars in the augmentor.
High performance military aircraft typically include a turbofan gas turbine engine having an afterburner or augmentor for providing additional thrust when desired. The turbofan engine includes, in serial flow communication, a multistage fan, a multistage compressor, a combustor, a high pressure turbine powering the compressor, and a low pressure turbine powering the fan. During operation, air is compressed in turn through the fan and compressor and mixed with fuel in the combustor and ignited for generating hot combustion gases which flow downstream through the turbine stages which extract energy therefrom. The hot core gases are then discharged into an augmentor from which they are discharged from the engine through a variable area exhaust nozzle.
The augmentor includes an exhaust casing and a liner therein circumscribing a combustion zone. Fuel spray bars and flameholders are axially located between the turbines and an exhaust nozzle at a downstream end of the combustion zone for injecting additional fuel when desired during reheat, thrust augmentation, or afterburning operation for burning in the augmentor combustor for producing additional thrust. Augmentor operation includes fuel injection into an augmentor combustion zone and ignition is initiated by some type of spark discharge or other igniter or auto-ignition due to hot core gases. Since the rate of gas flow through an augmentor is normally much greater than the rate of flame propagation in the flowing gas, some means for stabilizing the flame is usually provided, else the flame will simply blow out the rear of the engine, and new fuel being injected will not be ignited.
Various types of flameholders are used for stabilizing the flame and typically have included circumferential V-shaped gutters which provide stagnation regions there behind of local low velocity regions in the otherwise high velocity core gases for sustaining combustion during reheat operation. Radial spray bars have typically been used for injecting fuel for thrust augmentation.
In regions immediately downstream of the flameholder, the gas flow is partially recirculated and the velocity is less than the rate of flame propagation. In these regions, there will be a stable flame existing which can ignite new fuel as it passes. Unfortunately, flameholders in the gas stream inherently cause flow losses and reduced engine efficiency. Several modern gas turbine engine's and designs include radially extending spray bars and flameholders in an effort to improve flame stability and reduce the flow losses. Radial spray bars integrated with radial flameholders are disclosed in U.S. Pat. Nos. 5,396,763 and 5,813,221. Radial spray bars disposed between radial flameholders having integrated radial spray bars have been incorporated in the GE F414 and GE F110-132 aircraft gas turbine engines. This arrangement provides additional dispersion of the fuel for more efficient combustion and unload fueling of the radial flameholders with the integrated radial spray bars so that they do not blowout and or have unstable combustion due to excess fueling.
High levels of swirl may be produced in the exhaust flow downstream of the engine's turbines. Flow deflected off highly angled sides of radial flameholders impart considerable swirl to the exhaust flow and this imparted swirl is detrimental to thrust and stable combustion. Thus, it is highly desirable to have an augmentor or afterburner that can produce a stable flame and holding down thrust and flow losses due to swirl produced downstream of the turbines.